So what’s the sweet spot? According to a new study presented on Sunday at the European Society of Cardiology Congress, the ideal length of a night of sleep is six to eight hours—at least where heart health is concerned.

Dr. Epameinondas Fountas of the Onassis Cardiac Surgery Centre in Athens and his colleagues employed a meta-analysis of 11 recent prospective studies of more than one million adults (1,000,541) without heart disease to determine the impact that sleep has on the cardiovascular system.

The researchers compared people who slept for less than six hours a day, more than eight hours a day, and six to eight hours a day, and found that the sleep-deprived group had an 11 percent greater risk of developing cardiovascular disease. What might surprise you is that those who slept too much had an even greater risk–33 percent—corroborating with recent research that says that getting more than 8 hours of rest per night could be detrimental to your health.

“Our findings suggest that too much or too little sleep may be bad for the heart. More research is needed to clarify exactly why, but we do know that sleep influences biological processes like glucose metabolism, blood pressure, and inflammation—all of which have an impact on cardiovascular disease,” Fountas said. “Having the odd short night or lie-in is unlikely to be detrimental to health, but evidence is accumulating that prolonged nightly sleep deprivation or excessive sleeping should be avoided.”